in plasma-store/src/tests.rs [280:290]
fn plasma_client_create_error() {
let pc = build_client();
// put an object into the store
let oid = ObjectId::rand();
let data = [1u8, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16];
pc.create_and_seal(oid.clone(), &data, &[]).unwrap();
// try to create an object with the same ID
assert!(pc.create(oid.clone(), 16, &[]).is_err());
}